(CBS/AP) STOCKTON - Convicted California serial killer Wesley Shermantine says he knows where additional victims are buried, while also apologizing for taking years to reveal where he disposed of the bodies of two of his victims.

During an interview at San Quentin State Prison's death row with a reporter for the Stockton Record, Shermantine said Saturday that he was sorry it took so long for authorities to find the remains of Cyndi Vanderheiden, 25, and Chevelle Wheeler, 16, but denied that he had killed them.

"I'm sorry I buried their loved ones," Shermantine told reporter Scott Smith. "In no way, shape or form did I kill them," he said.

Vanderheiden disappeared in 1998, while Wheeler disappeared in 1985.

Authorities found Vanderheiden's and Wheeler's remains earlier this month with the help of a map provided by Shermantine, who was motivated by a bounty hunter's promise to pay him $33,000 for the information.

During Saturday's interview, Shermantine also said there were additional victims buried in Modesto, Stockton, Ripon and Milton. He said he would provide more details in future letters.

Shermantine and accomplice Loren Herzog were dubbed the "Speed Freak Killers" for their meth-fueled crime sprees in the 1980s and 1990s.

Shermantine was convicted of four murders and sentenced to death.

Jurors found Herzog guilty of three murders, but those convictions were later overturned after a judge determined his confession was illegally coerced. He instead struck a plea deal on one count of voluntary manslaughter and was paroled in 2010.

Herzog died in an apparent suicide last month, hours after receiving a call from bounty hunter Leonard Padilla warning him that Shermantine planned to reveal the burial locations.

Shermantine has been corresponding with The Record for six years in an exchange of letters that increased in frequency and detail beginning late last year.

His interview comes after more human remains were recovered Thursday near the site where the remains of Vanderheiden and Wheeler were found.

Shermantine has also led authorities to a well in San Joaquin County where investigators have recovered hundreds of human bone fragments.